Peony or paeony is a name for plants in the genus Paeonia, the only genus in the flowering plant family Paeoniaceae. They are native to Asia, southern Europe and western North America. Boundaries between species are not clear and estimates of the number of species range from 25  to 40.
Most are herbaceous perennial plants 0.5–1.5 metres tall, but some resemble trees up to 1.5–3 metres tall. They have compound, deeply lobed leaves, and large, often fragrant flowers, ranging from red to white or yellow, in late spring and early summer.
The family name "Paeoniaceae" was first used by Friedrich K.L. Rudolphi in 1830, following a suggestion by Friedrich Gottlieb Bartling that same year. The family had been given other names a few years earlier. The composition of the family has varied, but it has always consisted of Paeonia and one or more genera that are now placed in Ranunculales. It has been widely believed that Paeonia is closest to Glaucidium, and this idea has been followed in some recent works. Molecular phylogenetic studies, however, have demonstrated conclusively that Glaucidium belongs in Ranunculaceae, but that Paeonia belongs in the unrelated order Saxifragales.
Intersectional peonies are crosses between tree and herbaceous types. They have the leaf form of the tree peony, but die back, have a bush form, but are shorter than herbaceous peonies. 
Chemistry and Biological Activities
Over 262 compounds have been obtained so far from the plants of Paeoniaceae. These include monoterpenoid glucosides, flavonoids, tannins, stilbenes, triterpenoids and steroids, paeonols, and phenols. Biological Activities include Antioxidant, Antitumor, Antipathogenic, Immune-System-Modulation Activities,Cardiovascular-System-Protective Activities and Central-Nervous-System Activities.
This varies according to type, For instance Tree peonies are propagated by grafting but Herbaceous and Itoh peonies by root division. However new peonies are raised from seed. 
* Herbaceous species (about 30 species)
* Woody species (about 8 species)
Symbolism and uses
The peony is among the longest-used flowers in ornamental culture and is one of the smallest living creature national emblems in China. Along with the plum blossom, it is a traditional floral symbol of China, where the Paeonia suffruticosa is called 牡丹 (mǔdān). It is also known as 富贵花 (fùguìhuā) "flower of riches and honour," and is used symbolically in Chinese art. In 1903, the Qing Dynasty declared the peony as the national flower. Currently, the Republic of China on Taiwan designates the plum blossom as the national flower, while the People's Republic of China has no legally designated national flower. In 1994, the peony was proposed as the national flower after a nationwide poll, but the National People's Congress failed to ratify the selection. In 2003, another selection process has begun, but to date, no choice has been made.
The famous ancient Chinese city Luoyang has a reputation as a cultivation centre for the peonies. Throughout Chinese history, peonies in Luoyang are often said to be the finest in the country. Dozens of peony exhibitions and shows are still held there annually.
In Japan, Paeonia lactiflora used to be called ebisugusuri ("foreign medicine"). In kampo (the Japanese adaptation of Chinese medicine), its root was used as a treatment for convulsions. It is also cultivated as a garden plant. In Japan Paeonia suffruticosa is called the "The King of flowers" and Paeonia lactiflora is called the "prime minister of flowers."
Pronunciation of 牡丹 (peony) in Japan is "botan." Before the Meiji period, meat taken from quadrupeds was seldom consumed in Japan due to Buddhism. Thus in cases where such meat was handled, it was paraphrased using the names of flowers. The term botan was used (and is still used) to paraphrase wild boar meat. This comes from the flowery resemblance of the sliced meat when spread over a dish. Another example is sakura (cherry blossoms) which stands for horsemeat.
In 1957, the Indiana General Assembly passed a law to make the peony the state flower of Indiana, a title which it holds to this day. It replaced the zinnia, which had been the state flower since 1931.
Mischievous nymphs were said to hide in the petals of the Peony thus causing this magnificent flower to be given the meaning of Shame or Bashfulness in the Language of Flowers. It was named after Paeon, a physician to the gods, who obtained the plant on Mount Olympus from the mother of Apollo. Once planted the Peony likes to be left alone and punishes those who try to move it by not flowering again for several years. Once established, however, it produces splendid blooms each year for decades (Taken from The Language of Flowers, edited by Sheila Pickles, 1990).
Peonies are also extensively grown as ornamental plants for their very large, often scented flowers. Due to their colorful and attractive flowers, Peonies have gained a huge popularity these days and are also made available in artificial form which are used as indoor decoration.
Peonies tend to attract ants to the flower buds. This is due to the nectar that forms on the outside of the flower buds, and is not required for the plants' own pollination or other growth.
Peonies are a common subject in tattoos, often used along with koi-fish. The popular use of peonies in Japanese tattoo was inspired by the ukiyo-e artist Utagawa Kuniyoshi's illustrations of the Suikoden, a serialized novel from China. His paintings of warrior-heroes covered in pictorial tattoos included lions, tigers, dragons, koi fish, and peonies, among other symbols. The peony became a masculine motif, associated with a devil-may-care attitude and disregard for consequence.
1. ^ a b c Josef J. Halda and James W. Waddick. 2004. The genus Paeonia. Timber Press: Oregon, USA.
Source: Wikipedia, Wikispecies: All text is available under the terms of the GNU Free Documentation License